1. Field
The following disclosure is generally concerned with semiconductor laser type optical sources and more specifically concerned with high performance tunable laser oscillators having quantum well type gain media.
2. Related Technology
An optically pumped quantum well laser having wide tunability range is presented by Kaspi in U.S. Pat. No. 6,553,045. Inventor Kaspi presents structures which permit simultaneous lasing on two wavelengths and wavelength selection performed by ‘external’ means.
Another external cavity QCL system is presented in a CLEO paper titled: “Quantum cascade external cavity laser systems in the midinfrared spectral range” by Hildebrandt et al, published 2004 by the Optical Society of America. In this presentation, mention specific to anti-reflection coatings effect on the tunable nature of QCLs combined with external cavity elements is made. Hildebrandt also introduces an ECQCL in an abstract of paper titled: “Quantum cascade external cavity and DFB laser systems in the mid IR spectral range: devices and applications” published by the Optical Society of America, 2004.
QCL pioneer Faist, published a summary document with very specific description relating to QCLs in various configurations including single mode tuning of some DFB devices. In addition, one section is directed to “broadband and external cavity” arrangements. Further, in a similar paper titled “THz and Mid-IR Quantum cascade lasers” Faist includes a section on broadband tuning (at page 13). This is accomplished via an external cavity arrangement. Faist additionally leads a research group at the Institute of Physics in Neuchatel, Switzerland which published a paper: “Broadly tunable external cavity quantum-cascade lasers” where bound-to-continuum structures suitable for broadband use are mentioned.
“Recent updates in QCL-based sensing applications” is the title of a paper by Joel Hensley from Physical Sciences Inc., of Andover, Mass. where discussion regarding an enhanced tuning range of QCL lasers is mentioned. The same Hensley further describes QCL systems in a paper titled “Demonstration of an External Cavity Terahertz Quantum Cascade Laser”— published by the Optical Society of America, 2005.
Inventors Pham et al teach in U.S. Pat. No. 7,061,022 published Jun. 13, 2006, special laterally disposed heat spreading layers for epi-side up semiconductor lasers. While suggesting excellent heat management technique, the presentation clearly promotes epi side up as the best arrangement.
A laser diode is presented in an epi-down mounted configuration by Yamabayashi et al in U.S. Pat. No. 6,575,641 published Jun. 10, 2003. The laser enjoys a good thermal contact with a bulk base substrate operable for extracting to heat from the laser thus improving its performance.
U.S. Pat. No. 5,082,799 presented by inventors a Holmstrum et al., entitled “Method for fabricating indium phosphide/indium gallium arsenide phosphide buried heterostructure semiconductor lasers” These systems include semiconductor lasers arranged in an epi-down configuration. Moreover, these systems are presented in view of improving tuning range. The author notes a bandwidth of 24 GHz and has been observed.
Stephane Blaser presents a summary on QCL systems including those room temperature systems mounted in an epi-side down configuration. The presentation was made as: “Photonics West 2006—Novel In-Plane Semiconductor Lasers V: Quantum Cascade Lasers: 6133-01” Room temperature QCLs were first realized partly due to the improved heat extraction affored by epi-down mounted configurations.
Another practitioner group from the INFM—University of Bari in Italy similarly presents a discussion on using QCLs in an epi-down mounted configuration. Their paper titled: “Micro-probe characterization of QCLs correlation with optical performance”. A comparison is made between similar devices in epi-up and epi-down configurations; the comparison indicates heat extraction advantages.
Corrie Farmer's PhD thesis: “Fabrication and Evaluation of—In0.52Al0.48As/In0.53Ga0.47As /InP—Quantum Cascade Lasers”; University of Glasgow; September 2000, documents some analysis he has performed on QCL devices including experimentations on epi-up and epi-down mounted lasers. Mr. Farmer has mounted a QCL structure epi-down directly onto a copper heat sink to achieve high performance heat transfer.
“Improved performance of quantum cascade lasers through a scalable, manufacturable epitaxial-side-down mounting process” is the title of a paper supported by DARPA contract HR0011-C-0102, which shows exceptional comparisons between epi-up mounted and epi-down mounted QCL systems in a Proceedings of the National Academy of Sciences publication dated March 2006. A second similar publication in the Proceedings of the National Academy of Sciences dated July 2006 is directed to sub-parts-per-billion detection of NO2 using room temperature QCLs. These systems include continuously tunable external cavity QCLs.